The emf of the following galvanic cells with stabilized zirconia solid electrolyte was measured to determine the calcium antimonites which can coexist with liquid antimony in the temperature range 930−1100 K; (−)Pt, Re|Sb(1), two phases in CaO‐Sb2O3 system | O2− | air, Pt(+) Equilibrium oxygen pressures are obtained as follows:
3/2RT In PO2/kJ = −687.5+0.2433 T/K±0.6 for Sn, Sb2O3;
−817.8+0.2402T/K±0.6 for Sb(1), 4CaO·Sb2O3, CaO;
−800.5+0.2463T/K±0.6 for Sb(1), 4CaO·Sb2O3, 2CaO·Sb2O3;
−762.5+0.2828T/K±0.5 for Sb(1), 2CaO·Sb2O3, CaO·Sb2O3;
−690.5+0.2436T/K±1.0 for Sb(1), CaO·Sb2O3, Sb2O3.
Standard Gibbs free energies of formation of double oxides coexisting with liquid antimony from CaO(s) and Sb2O3 are derived as follows:
4CaO(s)+Sb2O3(1)=4CaO·Sb2O3(s); ΔG°/kJ = −130.3−0.0031 T/K
2CaO(s)+Sb2O3(1)=2CaO·Sb2O3(s); ΔG°/kJ = −121.7−0.00005 T/K
CaO(s)+Sb2O3(1)=CaO·Sb2O3(s); ΔG°/kJ = −98.3+0.0197 T/K.
The activities of Sb2O3 and CaO in the two phase regions at 1000 and 1100 K are derived and the most stable double oxide is CaO·Sb2O3 in this system. By an X‐ray diffractometry, it was found that 3CaO·Sb2O3(s) cannot coexist with Sb(1).